1. Field of the Invention
This invention relates to an improved coupling for joining together the end portions of a pair of conduits and more particularly to a coupling that is securely engaged to the conduits to prevent separation of the conduits from the coupling when axial forces are applied to the conduits.
2. Description of the Prior Art
Conventional couplings for joining together electrical conduits, pipes and the like typically include a cylindrical body with an internally threaded portion for receiving the respective end portions of conduits to be joined together by the coupling. The coupling includes an internal passageway having threaded end portions or ridged sections to permit advancement of each conduit end portion through the passageway and into engagement therewith. The coupling is secured to the threaded end portion of one conduit, and then the engaged coupling and conduit are rotated to advance the other threaded conduit into the coupling to join together the conduits. However, with this arrangement because the ends of the coupling are threaded, the end portions of the conduits must rotate. This presents a considerable problem particularly in the case of long conduits and arcuately shaped conduits where it is not possible to rotate the conduits to effect coupling thereof.
A conventional coupling having threaded end portions is also expensive to manufacture. Once the respective threads or ridges are machined for both sections of the coupling, the versatility of the coupling is substantially reduced. Not only is the coupling limited to joining conduits of a fixed diameter, the threaded end portions of the conduits must be rotated to advance the conduits into meshing engagement with the respective internally threaded portions of the coupling.
U.S. Pat. No. 1,794,849 discloses an electric conduit coupling that includes an annular internal groove of a preselected depth that separates a threaded portion from a ridged portion of the coupling. A pipe end portion is inserted into the ridged end of the coupling until the end wall of the pipe engages a shoulder formed by the innermost thread of the threaded section of the coupling that abuts one side of the annular internal groove. A tapered punch is secured to the threaded end of the coupling and struck to spread the pipe into the recess formed by the annular internal groove. The adjoining threaded pipe is advanced in the threaded end of the coupling to abut the end of the pipe expanded into the annular internal groove. The end portions of the pipes are secured within the coupling by expanding one end portion into the internal annular groove and securing the other end portion by threaded engagement with the threaded portion of the couplings. Even though the end portions of the pipes are secured to the coupling, the end portions merely butt and are not secured to each other any may consequently be loosened from engagement with the coupling.
In United States application, Ser. No. 622,863 filed Oct. 16, 1975, entitled "Conduit Coupling", now abandoned, a coupling for joining together the end portions of conduits, pipes and the like is disclosed and includes a sleeve member having an internally threaded portion that is separated from a cylindrical passageway by a tapered annular portion. The diameter of the tapered annular portion progressively increases from the cylindrical passageway to the threaded portion. The end portion of a first conduit to be joined is extended through the small diameter end of the tapered annular portion and flared outwardly into the annular portion. The flared end portion is rotatable relative to the sleeve but is restrained from axial movement out of the sleeve by contact with the shoulder of the tapered annular portion. A second conduit is threadedly engaged to the threaded end portion of the sleeve by rotation of the sleeve. The end portion of the second conduit is urged into underlapping engagement with the flared end portion of the first conduit, in turn, urging the first conduit into engagement with the sleeve annular portion. With this arrangement the first conduit is secured within the sleeve.
There is need for a coupling for joining the end portions of pipes, conduits and the like in which the coupling joins the conduit end portions in locking engagement sufficiently to withstand axial forces that when applied to the conduits tend to separate the conduits from connection with the coupling. While it has been suggested to threadedly secure the conduit end portions to the coupling and to provide locking engagement of the conduits to the coupling, the prior art devices require the conduits to be rotated into the coupling.